The human spine serves many functions. The vertebral members of the spinal column protect the spinal cord. Furthermore, moveable facet joints and resilient discs disposed between the vertebral members permit motion between individual vertebral members. The spinal column also supports other portions of the human body. When viewed from a posterior or anterior direction, the vertebral members are generally aligned, although the width of the vertebral members generally increases from the cervical region to the lumbar region. However, when viewed from a lateral direction, the spine is curved to absorb loads and maintain the balance of the upper body. Abnormal curvatures may occur in some patients. For example, kyphosis may describe an exaggerated posterior curvature in the thoracic region. Lordosis may describe an exaggerated anterior curvature of the lumbar region. Scoliosis may describe an abnormal lateral curvature.
The composite sum of the angular relation between adjacent vertebral members makes up the overall curvature of the spine. Thus, one technique to correct abnormal spinal curvatures is to insert interbody implants that include a desired correction angle between vertebral bodies in the spine. The correction angle may be in the coronal plane or the sagittal plane. It is certainly possible to include implants that provide both coronal and sagittal correction of multiplanar defects. For example, a single interbody implant may provide a desired angular correction in the coronal plane and a separate desired angular correction in the sagittal plane. An implant with this configuration provides a compound correction that is the vector combination of the two corrections. A full set of implants may be provided that account for all possible corrections in both coronal and sagittal planes. However, when one considers the number of correction angles that are possible in both directions, it becomes impractical to manufacture, stock, and have available all of the possible combinations for implantation into a patient. Furthermore, implants that provide correction in both coronal and sagittal planes provide a unique combination of correction angles that are likely unusable in most cases.